Polarized electromagnet



June 21, 1949.-

POLARIZED ELECTROMAGNET Filed Oct. 22, 1945 w. B. M. CLARK- 2,473,939 L Patented June 21, 1949 STATES PATENT ;()-IFFICE POLARIZEDELECTROMAGNET Winslow Clark,*West Orange, N. J assignor to "Thomas A. Edison, incorporated, West Orange, N. J.,.a corporation of New.Ierse-y .iApplicationOctbberZZ, 1945,,Serial No. 623,795

6v Claims.

. 1 This. invention relates to meter=type electrical instruments and, more particularly to instruments of this character which use permanent-magnet rotors. By way of illustration, the invention is herein shown andldes'cribed in terms of a sensitive meter relay, but it" will be understood that in many of its features the invention has application as well toelec trical measuring instru-- ments.

Certain features of the present illustrative embodiment of myinvent'ion are described and claimed in the pending 'Foxapplication Serial No. 540363, filed June 14,1944, now Patent No. 2439;970, granted April 20, 194:8,and having a common assigneewith the present application. It is an object of'my invention to provideimprovements in the construction of meter-type electrical instruments of the character mentioned. It is another object-to provide a meter relay of the moving magnet typewhich ischaracterized ashaving ahigh sensitivity, a highly dependable operation and a simple-and economical .construction.

Further objects of my invention are to provide an improved construction of electrical instrument of the moving-magnet type wherein both jewel bearings are removable without disturbing the mounting ofthe-shield or field coilsgthe shield is accurately located in symmetrical relation to the pivot axis of the rotor and the rotor isremovable without "disturbing the mounting of the field coils'and shield.

These and other objects and features of .my invention will be apparent from the following description and the appended claims.

In the description of my invention reference is had to the accompanying drawings, of which:

Figure l is a principally axially sectional view of a meter relay according to my invention;

- Figure 2 is'a-sideelevatimxof thexmeter relay less the housing andshowing the shield broken :away;

' "Figure -3 is'a' section. takensubstantially 2011 figures comprises a'ma-gnet ;l0, .preferably 'ofa 'bar shape asshown, mountedton ,a shaft! I. The shaft has pivots :.li2,:.ata the ends thereof which pivotallyrengage lower andupperybearings I 3 and c'lflliypically of: the ;:M ::iewe11type.. :The ma net :28 is countersunk l :at 18a,

ispositioned withina damping cup "l5 made of a'conductive material such as'copper orbr'ass. This damping cup-has a dependingtubular stem 16 in which is mounted the lower jewel. 13. The dan'rpi-ng'cup is housed 'in'a frame member 11, preferably an aluminum casting, which has an axial opening I8 ofenlargeddiameter extending partially therethrough and an axial opening IQ of reduced diameter extendingthrough' the remaining length thereof. The damping cup [5 is positioned-at thebottom of the enlarged axial opening 18 and the stem [6 snugly fits the-smaller opening 19 and projects beyond the bottom wall of the frame member. The frame-member has a circular head We provided with two upstanding posts 2 0. These-posts support the bridge 2'! in which is threaded 'the topjewel 14. Below the head Ila the frame member is provided with a narrow portio-nl-lb having flat parallel sides opposite the pivot axis "of the rotor. In the side spacesbelow the head I la there are two field coils 2'2 having spools 23 seated against the opposite sides of the 'frame portion lib. These spools have recesses 24 in their inner side walls which are engaged by portions of the damping cup [5 whichoverhang the frame portion I lb. Byt'nis engagement of the damping cup with thespools the coils are accurately located.

Thewidth of the frame portion 51b is preferably at. least as great as'the Width of the magnet- 16. Thus, upon removing the bridge 25 and turning the magnet to a position wherein its longitudina1 geometrical axis is parallel with the Pfield coils, the magnet may be lifted out of the housingthrough the-opening 18' while the coil-s are in their mounted positions.

The bottom face-of thehead-lia of the frame member is conical: to provide a seat 25 for one end of .a tubular magnetic shield 26. Below the frame member there is a circular base 27 of insulating: material having a central opening 28 for receiving the stem Hi. This base has an annular shoulder- 29 snugly fitting the interior Wall of the shield 26 and haste-n annular face 30 in va plane atright angles to the pivot axis of the instrument which abuts against the end of the shield, this shoulder and face constituting a seat for the lower end of the shield. The opening and threaded exteriorly onto the stemldis-a conical nut 31 which engages'this countersinktoclamp the basel! "tightly against the shield. and: to centralize the base relative to the: pivot .axis. and retain it at right. angles thereto. while :Ithave. described the base. 21. as. lhav 'mjg the annular shoulder 29 I may rely wholly on the annular face 30 for localizing the shield at the bottom, in which case I may dispense with the shoulder. However, when the face 30 is used as the sole means for localizing the shield at the bottom, it is important that both end faces of the shield be parallel to one another in planes at right angles to the center axis of the shield.

Between the coil spools 23 and shield 26 there are U-springs 32 for holding the spools seated against the frame member. These springs have inwardly-extending end portions which engage axial holes 33 in the spools for retaining the springs in place.

The jewel I3 is urged upwardly by a spring 34 against an internal seat 35 within the stem IS, the spring 34 being backed by a screw 36 which is threaded into the stem. Threaded into the outer portion of the stem is a headed screw 31 which bears against the nut 3| to lock the latter in place.

It will be seen that in the above construction the bottom jewel I3 may be removed simply by unthreading the screws 31 and 36 without loosening the base 21 or disturbing the mounting of the shield or coils. This is very advantageous since it permits replacement of the jewel without disturbing the calibration or adjustment of the instrument.

Mounted on the shaft |I near the top thereof is a balance cross 38 which carries weights 3!! for balancing the rotor of the instrument. Turned up from this balance cross is a lug 40 and secured thereto as by soldering is the inner end of a spiral spring 4|. The outer end of this spring is anchored to a downwardly-turned arm 42 of the terminal 43 which embraces the jewel l4 and is secured against the top side of the bridge 2| by a nut 44 threaded onto this jewel. Below the balance cross 38 there is a contact arm 45, preferably of platinum, which is secured as by soldering to the shaft ll. Spaced counterclockwise from the contact arm 45 is a semi-stationary contact arm 43 having an end portion lyingin the path of the arm 45; this contact arm 46 constitutes preferably a thin platinum wire. The contact arm 46 is secured as by soldering to a terminal 41 which is riveted to the bridge 2|. Preferably the bridge 2| is made of an insulating material such as Bakelite so that insulation is not required between it and the two terminals 43 and 41.

In the construction described in the foregoing paragraph the spring 4| serves as a biasing means for holding the rotor in an initial position defined for example by the abutment of one of the arms of the balance cross against an insulating sleeve 48 supported by an arm 49 from one of the posts 23 as shown in Figure 3. Also, the spring 4| electrically connects the moving contact arm 45 to the stationary terminal 43. (While the arm 45 is electrically connected to the shaft II, and this shaft is typically made of metal, the arm is electrically insulated from the instrument frame by the jewels i4 and I3, which are typically made of glass.)

The contacts 45 and 46 constitute the switch for the present relay. When the coils are energized to propel the rotor counterclockwise from its initial position above described the contact arm 45 strikes the contact arm 46 and deflects the latter to make a rolling sliding contact therewith; likewise, when the current supply to the relay is cut off the rotor is returned clockwise to initial position by the spring 40 and the contacts are broken again with a relative rolling sliding movement. In view of the rolling movement between the contacts a small return force is effective to break the contacts apart even though they may have been fused together over a limited area by the current which they control.

When the rotor is in initial position the magnet |0 lies in the position approximately shown in Figure 5 wherein its magnetic axis-which corresponds with its longitudinal geometrical axisis at a minor fraction of a right angletypically 30from the magnetic axes of the coils 22. The coils are serially connected in magnetically aiding relation and are so polarized that when energized the magnet is propelled counterclockwise. The spacing between the contact arms 45 and 46 is typically such that they close when the magnet is approximately at right angles to the aXes of the coils. This is the most eifective position of the magnet for closing the contacts since herein the coils have a maximum torque influence on the magnet per unit of energizing current. As a typical example, it may be noted that the present relay is designed especially for thermostatic fire-alarm systems on aircraft, and has proven to work dependably in this application despite extreme vibration and widely varying temperatures, from as little power as 25 microwatts the power of a single thermocouple. For this application the field coils are serially connected in magnetically aiding relation and a single-pole single-throw switch is employed, as described. It will be understood, however, that for other applications the coils may be differentially connected and/or the instrument may be provided with a second semi-stationary contact such as the contact 46 so as to form a single-pole double-throw type of relay,

The present relay is adapted for socket mounting by providing the base with a series of depending pins 5El. In the present example, there may be six such pins. The coils 22 are connected to four of these pins by wires 5| which are anchored in the coil spools and which extend downwardly through the pins, the wires being secured to the latter as by soldering. The other two pins are connected by a pair of twisted wires 52 which lead up through the housing at 53 to the terminals 43 and 41. Mounted on the base 21 and covering the entire instrument is a cover 54 which is made of metal or suitable plastic.

While I have herein shown and described my invention in terms of a preferred embodiment thereof, it will be understood that this embodiment is subject to changes and modifications without departure from the scope of my invention, which I endeavor to express according to the following claims.

I claim:

1. In an electrical instrument including a Pivoted permanent magnet, means for generating a magnetic field to produce a torque influence on said magnet, and a cylindrical magnetic shield surrounding said magnet; means for locating said shield in concentric relation to the pivot axis of said magnet, comprising a seating member having a conical face centered at said pivot axis for locating one end of said shield; a second seating member having an annular shoulder centered at said pivot axis and adapted to fit the interior wall at the other end of said shield and further having an abutment face in a plane at right angles to said pivot axis adapted to bear against said other end of the shield; and means for clamping said seating members, in directions 5 along said pivot axis, against the ends of said shield.

2. In an electrical instrument comprising a pivoted magnet and a surrounding magnetic shield: a frame structure for pivotally supporting said magnet and holding said shield centered in relation to the pivot axis of the magnet, comprising a main frame portion having a seat for one end of said shield, an axially located tubular element fixedly secured to said main frame portion and extending beyond said shield, a pivot bearing for said magnet removably mounted within said tubular element, a separate rem-ovable seating and centralizing member for the other end of said shield centrally apertured to receive said tubular element, means secured in said tubular element for retaining said bearing in mounted position, and separate means externally secured to said tubular element for securing said seating member to said main frame portion and clamping the same against said shield.

3. In an electrical instrument comprising a pivoted magnet and a surrounding cylindrical shield: the combination of a frame for said instrument having an integral portion forming a seat for one end of said shield; a pivot bearing for said magnet mounted removably on said frame at the other end of said shield; and a shield-locating member having an annular seat for said other end of said shield and removably secured to said frame, said locating member having an opening through which said pivot bearing is removable without disturbing the mounting of said shield and said locating memher being mounted independently on said pivot bearing.

4. In an electrical instrument including a pivoted permanent magnet, electromagnetic means for producing a torque influence on said magnet, and a surrounding tubular magneti shield: the combination of a frame for said instrument insertable into said shield and having a seat for the inner end of the shield; an axial element projecting from said frame beyond the other end of said shield; means pivotally supporting said magnet at the central axis of said frame; a member having an annular seat for the other end of said shield and having a central hole countersunk in its outer wall, said axial element engaging said hole; and a conical nut exterior- 1y threaded onto said axial element for clamping said member against said shield.

5. In an electrical instrument including a pivoted permanent magnet, electromagnetic means for producing a torque influence on said magnet, and a surrounding tubular magnetic shield: the combination of a frame for said instrument insertable into said shield and havin a seat for the inner end of the shield, a tubular element projecting from said frame beyond the other end of said shield, a pivot bearing in said tubular element for said magnet, a shield-localizing member having an annular seat for the other end of said shield and having a central hole received by said tubular element, a nut exteriorly threaded onto said tubular element to clamp said locating member against said shield, and means threaded into said tubular element and bearing against said nut for locking the latter in place.

6. In an electrical instrument including a pivoted permanent magnet: the combination of a tubular shield surrounding said magnet and having end faces in planes at right angles to its central axis, a conical seating member centered at the pivot axis of said magnet and having its medial plane at right angles to said pivot axis for locating one end of said shield, a second seating member having a flat face at right angles to said pivot axis for abutting against the face at the other end of said shield, and clamping means for pressing the said seating members along said pivot axis against the ends of said shield.

WINSLOW B. M. CLARK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 698,027 Knap Apr. 22, 1902 1,452,591 Brogger Apr. 24, 1923 2,145,821 Wallace Jan. 31, 1939 2,339,021 Lingel Jan. 11, 1944 2,345,011 Sias Mar. 28, 1944 2,437,726 Davis Mar. 16, 1948 2,446,579 Fritzinger Aug. 10, 1948 

